The present invention relates to diamino compounds and liquid crystal alignment layers obtained from the compounds, more particularly, new diamino compounds, a method for producing the compounds, liquid crystal alignment layers having high pretilt angles, which is obtained by using the diamino compounds, and liquid crystal display devices equipping the liquid crystal alignment layers.
The main current of liquid crystal display devices which are used in conventional clocks, watches and electronic calculators is a twist nematic (abbreviated as TN hereinafter) mode having a structure in which molecular alignment of nematic liquid crystals is twisted at an angle of 90 degrees on the surface of a couple of upper and lower electrode substrates. Further, a supertwist nematic (abbreviated as STN hereinafter) mode in which the molecular alignment of nematic liquid crystals is twisted at angles of 180-300 degrees has been developed and then large panel liquid crystal display devices having excellent display quality are developing.
Moreover, in recent years, since matrix display or color display has been done, a MIM (metal-insulation layer-metal) device and a TFT (field effect type thin layer transistor) device are developing, and the MIM device adopts many pixel electrodes and an active type twist nematic mode which can switch ON-OFF against these electrodes.
As to problems shared by these modes, when the same scene is lighted up for a long time, an image-sticking phenomenon may be found after the scene has disappeared. Particularly, it is very important problems to improve the image-sticking phenomenon to obtain a liquid crystal display devices having high quality.
It is considered that the image-sticking phenomenon is due to electric double layers which are produced on the alignment layers surface by ion components of impurities contained in the liquid crystal since DC components are applied on the liquid crystal display device electric charge differences which are produced between upper and lower substrates, and electric potential differences from the stable electric charge differences. Particularly, in case of TFT devices, since DC components cannot be removed for characteristics of the devices, the image-sticking phenomenon is more conspicuous and serious than that of TN and STN.
Further, in TFT modes, high voltage holding ratios are required to prevent flicker of screens.
As an alignment layer used for such a liquid crystal display device, organic films such as polyimide and polyamide are mainly employed, and Japanese Publication of Unexamined Patent Application No. 51-65960 discloses a liquid crystal display device that is equipped with a liquid crystal alignment layer produced from a polyimide resin having a repeating unit represented by a formula: ##STR2##
However, the polyimide alignment layer produced from such a polyether compound has a problem that the image-sticking phenomenon is apt to produce.